Question

If 5x - 2y = 7 and xy = 2 then , find the value of (5x + 2y)²

Answer 1

$( {5x - 2y})^{2} = 49 \\ 25 {x}^{2} + 4 {y}^{2} - 20xy = 49 \\ 25 {x}^{2} + 4 {y}^{2} = 49 + 20(2) \\ 25 {x}^{2} + 4 {y}^{2} = 89 \\ \\ ({5x + 2y})^{2} = 25 {x}^{2} + 4 {y}^{2} + 20xy \\ = 89 + 40 \\ = 129 \: is \: the \: ans$